Trisomy 13

Trisomy 13, also known as Patau syndrome, is a rare genetic disorder caused by the presence of an extra copy of chromosome 13.

Causes and Risk Factors

Trisomy 13 occurs when there is an error in cell division during fertilization or early fetal development, resulting in an extra copy of chromosome 13. This can happen in one of two ways:

• Free trisomy 13: This is the most common form, where every cell in the body has an extra copy of chromosome 13.
• Mosaic trisomy 13: This occurs when only some cells have the extra chromosome 13, while others have the normal number of chromosomes.
• Translocation trisomy 13: This is a rare form where part of chromosome 13 breaks off and attaches to another chromosome.

The risk of having a child with Trisomy 13 increases with the mother's age, particularly over the age of 35.

Symptoms

Children born with Trisomy 13 often have severe physical and developmental abnormalities, including:

• Heart defects
• Cleft lip and palate
• Extra fingers or toes
• Rocky mountain spotted fever-like rash
• Small eyes or microphthalmia (underdeveloped eyes)
• Low-set ears
• Weak muscle tone (hypotonia)
• Developmental delays and intellectual disability

Many children with Trisomy 13 also experience seizures, vision and hearing loss, and feeding difficulties.

Diagnosis

Trisomy 13 can be diagnosed prenatally through:

• Chorionic villus sampling (CVS)
• Amniocentesis
• Ultrasound

After birth, a physical examination and genetic testing, such as karyotyping or chromosomal microarray analysis, can confirm the diagnosis.

Treatment and Management

There is no cure for Trisomy 13, but various treatments and interventions can help manage the symptoms and improve quality of life. These may include:

• Surgery to repair heart defects or cleft lip and palate
• Physical, occupational, and speech therapy to support development
• Medications to control seizures and other medical conditions
• Supportive care, such as feeding tubes and respiratory assistance, for children with severe disabilities

Prognosis

The prognosis for children with Trisomy 13 is generally poor. According to the National Institutes of Health (NIH), approximately 80% of children with Trisomy 13 do not survive beyond their first year, and only about 10% live beyond age 5.

Genetic Counseling

Genetic counseling can help families understand the risk of having another child with Trisomy 13. The recurrence risk is low, but it increases with the mother's age.